Telomerase, an enzyme involved in DNA replication, plays an important role in the development of cancers and appears to explain why cancer cells replicate so aggressively. The link between telomerase and cancer is of interest because it provides information about how cancers persist when the cells should stop growing, and also offers some insight into potential treatments. By targeting these enzymes with medications, a doctor could stop the growth of cancer cells in their tracks by exploiting the telomerase and cancer link.

In normal cells, DNA replication comes at a cost. The enzymes that duplicate the chromosomes cannot run all the way to the ends of the DNA chains. This would result in a constant clipping of genetic material, and a subsequent degradation of DNA with each cell division. Sections known as telomeres get around this problem by providing a series of repeats at the ends of the chromosomes. Cutting some of the repeats doesn’t damage the coding DNA at the core of the chromosome.

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With each cell division, the telomeres get shorter, even with telomerase present in the cell to add repeats during divisions to keep the DNA as stable as possible. Eventually, cells cannot reliably replicate anymore, and a cell line dies out. The number of divisions a cell is capable of can vary, and in the body at any given time, the cells may have telomeres of varying lengths. This built-in senescence is not just a recipe for aging. It also allows the body to shut cells down as their DNA becomes corrupted through multiple replications, because the sections are too short for the DNA to copy reliably.

Researchers studying cancer noted that tumor cells often contained these specific proteins. This demonstrated a clear link between telomerase and cancer, showing that tumor cells used the enzyme to make themselves effectively immortal. Cancer cells typically have very short telomeres, but the connection between telomerase and cancer ensures that the telomeres remain long enough for the cell to keep replicating, allowing a tumor to grow.

Jack W. Szostak, Carol Greider, and Elizabeth H. Blackburn, winners of the 2009 Nobel Prize in Medicine or Physiology, made an important discovery about telomerase and cancer. They found that cancer cells started producing telomerase after they became malignant. This explains why their telomeres become unusually short in the first place, as the enzyme isn’t present to add repeats during cell division at first. Once the cells start to get out of control, losing the checks on replication that would normally kill malignant cells, they use telomerase to keep growing.

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